Pathways Involved in EGF‐Stimulated LPA Production by Ovarian Carcinoma Cells

Abstract

Lysophosphatidic acid (LPA) refers to a family of small lipid mediators involved in diverse cellular processes. LPA binds to G-protein coupled receptors to induce cellular effects that include proliferation, angiogenesis, and migration and metastasis of tumor cells. Levels of LPA have been shown to be increased in the acites fluid surrounding ovarian tumors. Several enzymes are potentially involved in the production and metabolism of LPA, including phospholipase D (PLD), autotaxin (ATX), and acylglycerol kinase (AGK). However, the pathways and mechanisms that regulate LPA production are poorly understood. We have shown that epidermal growth factor (EGF) can stimulate LPA production. We hypothesize that EGF stimulates one or more phospholipase activities to increase LPA production. In this study, LPA levels in the medium increased within 30 minutes after addition of EGF to ovarian cancer cell lines, OVCAR3 and SKOV3. LPA receptor antagonist Ki16425 inhibits both LPA and EGF-induced LPA production in SKOV3 cells. Over-expression of PLD2 increases PLD activity, as does EGF, in OVCAR3 cells and membrane preparations. This over-expression also increases basal levels of LPA production. Levels of mRNA for ATX are reduced in OVCAR3 cells incubated with siRNA for ATX. However, ATX siRNA did not significantly inhibit basal or EGF-stimulated LPA production measured at 30 minutes. Both ovarian cancer cell lines express acylglycerol kinase, another enzyme potentially involved in LPA production. Together, these results suggest that multiple enzymes can participate in LPA production (Supported by DAMD17-01-1-0730).